# -*- coding: utf-8 -*-

"""
  UNIX daemon class.

  Referred to: A simple unix/linux daemon in Python by Sander Marechal
  Site URL: http://www.jejik.com/articles/2007/02/a_simple_unix_linux_daemon_in_python/ 
  It is LICENSEd by creative commons.
  Attributetion-ShareAlike 2.0 Unported (CC By-SA 3.0)
  Thank you for Sander Marechal.

  Referred to "Python Cookbook 2nd Edition" O'REILLY.
  Title: Forking a Daemon Process on Unix"
  Page: 388
"""

import sys
import os
import time
import atexit
from signal import SIGTERM

class Daemon(object):
  """
    A generic UNIX daemon class.

    Usage: subclass the Daemon class and override the run() method.
  """
  def __init__(self, pidfile, stdin='/dev/null', stdout='/dev/null', stderr='/dev/null'):
    self.stdin = stdin
    self.stdout = stdout
    self.stderr = stderr
    self.pidfile = pidfile

  def daemonize(self):
    """
      do the UNIX double-fork magic, see Stevens' "Advanced
      Programing in the UNIX Environment" for details (ISBN 0201563177)
      http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC16
    """
    try:
      pid = os.fork()
      if pid > 0:
        # exit first parent
        sys.exit(0)
    except OSError, e:
      sys.stderr.write("fork #1 failed: %d (%s)\n" % (e.errno, e.strerror))
      sys.exit(1)

    # Decouple from parent environment
    os.chdir('/')
    os.setsid()
    os.umask(0)

    # Perform second fork.
    try:
      pid = os.fork()
      if pid > 0:
        # exit from second parent
        sys.exit(0)
    except OSError, e:
      sys.stderr.write("fork #2 failed: %d (%s)" % (e.errno, e.strerror))
      sys.exit(1)

    # Flush stream.
    for f in sys.stdout, sys.stderr:
      f.flush()

    # redirect standard file descriptors
    si = file(self.stdin, 'r')
    so = file(self.stdout, 'a+')
    se = file(self.stderr, 'a+', 0)
    os.dup2(si.fileno(), sys.stdin.fileno())
    os.dup2(so.fileno(), sys.stdout.fileno())
    os.dup2(se.fileno(), sys.stderr.fileno())

    # write pidfile
    atexit.register(self.delpid)
    pid = str(os.getpid())
    file(self.pidfile, 'w+').write("%s\n" % pid)

  def delpid(self):
    os.remove(self.pidfile)
    self.pidfile = None

  def start(self):
    """
      Start the daemon.
    """
    # Check  for a pidfile to see if the daemon already runs.
    try :
      pf = file(self.pidfile, 'r')
      pid = int(pf.read().strip())
      pf.close()
    except IOError:
      pid = None

    if pid:
      message = "pidfile %s already exists. Daemon already running?\n"
      sys.stderr.write(message % self.pidfile)
      sys.exit(1)

    # Start the daemon
    self.daemonize()
    self.run()

  def stop(self):
    """
      Stop the daemon.
    """
    # Get the pid from the pidfile.
    try:
      pf = file(self.pidfile, 'r')
      pid = int(pf.read().strip())
      pf.close()
    except IOError:
      pid = None

    if not pid:
      message = "pidfile %s does not exists. Daemon not running?\n"
      sys.stderr.write(message % self.pidfile)
      return # not an error in a restart

    # Try killing the daemon process
    try:
      while 1:
        os.kill(pid, SIGTERM)
        time.sleep(0, 1)
    except OSError, err:
      err = str(err)
      if err.find("No such process") > 0:
        if os.path.exists(self.pidfile):
          os.remove(self.pidfile)
        else:
          print str(err)
          sys.exit(1)

  def restaart(self):
    """
      Restart the daemon.
    """
    self.stop()
    self.start()

  def run(self):
    """
      You should override this method when you subclass Daemon. It will be called after the process has been
      damonized by start() or restart().
    """
